Use of laser-excited atomic fluorescence spectrometry with a novel diffusive graphite tube electrothermal atomizer for the direct determination of silver in sea water and in solid reference materials

摘要

Laser-excited atomic fluorescence spectrometry is used with a novel diffusive graphite tube electrothermal atomizer for the determination of silver in sea water and three National Institute of Science and Technology (NIST) soil reference materials (SRM 2709, 2710 and 2711). The samples are contained in a small graphite boat which is attached to one of two graphite electrodes. The boat is inserted into the center of a graphite tube which is then sealed by the electrodes and heated. The vaporized sample diffuses through the heated graphite walls and is excited by a laser beam which passes a few mm above the tube. The seawater matrix causes a two-fold suppression in the silver fluorescence signal compared with a pure aqueous standard of the same concentration. The depression is constant over a concentration range of 6 orders of magnitude. When aqueous standards were used for the determination of Ag in the solid samples, no significant difference between the measured values and the certified values were found. A limit of detection of 40 fg (4 ppt) was obtained for pure aqueous solutions and 90 fg (9 ppt) in a 1:1 diluted seawater matrix. A concentration of silver of 14 ng L~(-1) was determined in a sample of coastal Atlantic water.